Studies will be directed toward assessing suppressor and helper functions affecting immune responses in patients with autoimmune thyroid disease, assessing the involvement of immune complexes in autoimmune thyroid disease, studying the natural history of autoimmune thyroid disease, and studying the effect of certain therapies on these diseases. Suppressor cell function will be measured after Con-A stimulation, radiation, removal by preculture, or exposure to Indomethacin, and determining the effect of the patient's lymphocytes on pokeweed mitogen stimulated responding B cells. We will study patients serially after diagnosis and during treatment and will have corresponding control groups of normal patients and patients with other thyroid disease. Populations of suppressor and helper T lymphocytes will be assessed by rosetting techniques and immunofluorescent microscopy. Specific suppressor cell function will be assessed by exposure of patient's lymphocytes to thyroglobulin for induction of suppressor activity determined in a responding allogenic B cell antibody producing lymphocytes culture. Thyroglobulin and microsomal immune complexes will be determined by a radiometric assay procedure in similar patient groups, and the presence of immune complexes will be correlated with the progress of the disease or the presence of other aspects of autoimmunity. Children of patients with Graves' disease will be studied serially over several years to detect evolution of the thyroid autoimmune process among individuals at high risk of developing thyroid disease. Similar studies will be done on patients who have entered remission from Graves' disease and are at risk of a relapse. We will study the effect of intermittent prednisone therapy on patients with thyrotoxicosis. Plasma-pheresis and cyclophosphamide therapy will be evaluated in patients with severe exophthalmos and severe pretibial myxedema. Coincident evaluation will be made of immune complexes, thyrotrophin displacing immunoglobulins, and suppressor cell function in these patients.